1. Field of the Invention
The present invention relates to a semiconductor laser module for coupling a laser beam emitted from a light source with an optical fiber, and to an optical scanner employing the semiconductor laser module.
2. Description of the Related Art
Semiconductor laser modules capable of maintaining an efficient coupling between a laser beam emitted from a semiconductor laser and a single-mode optical fiber have been widely used in the field of optical communications.
Generally, the core diameter of single-mode optical fibers decreases as the oscillation wavelength of the semiconductor laser is shortened. The core diameter is on the order of microns when using semiconductor lasers that emit visible light. Hence, precision in positioning an incident portion of the optical fiber and a laser beam emitted from a semiconductor laser, as well as environmental stability, after assembly of a module is even more severe in semiconductor laser modules that emit visible light than in optical communication modules.
When assembling modules that require such high precision in positioning, an optical fiber section is fixed using fixing means such as solder, adhesive, fusion, and welding. As disclosed in Japanese Patent Application Publication No. H11-54852, these fixing means may also be used to hermetically seal the optical fiber section.
Further, since a laser beam focused to an order of microns is constantly irradiated onto the incident end of the optical fiber in the semiconductor laser module, the light energy density is very high, and dust accumulating due to optical trapping of the laser beam (Ashkin, et al.: Observation of a Single-Beam Gradient Force Optical Trap for Dielectric Particles; Opt. Lett. 11, pp. 288-290, 1986) at the core of the optical fiber, which is the focal spot of the laser beam, leads to a drop in coupling efficiency with the optical fiber. In addition to optical trapping for lasers, this problem causes photochemical reactions between the accumulated dust and the laser beam when using a laser having a short wavelength no more than 450 nm near ultraviolet light range, leading to a more serious risk of contaminating the optical fiber.
As disclosed in Japanese Patent Application Publication No. H11-54852, contaminants may be produced when the laser beam polymerizes or degrades hydrocarbons introduced into the atmosphere during the production process or when the laser beam causes a photochemical reaction with airborne siloxane, resulting in the accumulation and deposition of contaminants in the form of SiOx. Hence, the Japanese Patent Application Publication No. H11-54852 proposes the periodic replacement of components that may become contaminated.
Japanese Patent Application Publication No. 2004-253783 proposes a method of controlling contamination on the incident end of the optical fiber. The semiconductor laser module is provided with a package that is hermetically sealed with a flux-free solder, an adhesive that does not contain silicon organics, or through fusion or welding to keep out contaminants.